# -*- coding:utf-8 -*-


# You are climbing a stair case. It takes n steps to reach to the top.
#
# Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top?
#
# Note: Given n will be a positive integer.
#
# Example 1:
#
#
# Input: 2
# Output: 2
# Explanation: There are two ways to climb to the top.
# 1. 1 step + 1 step
# 2. 2 steps
#
#
# Example 2:
#
#
# Input: 3
# Output: 3
# Explanation: There are three ways to climb to the top.
# 1. 1 step + 1 step + 1 step
# 2. 1 step + 2 steps
# 3. 2 steps + 1 step
#
#


class Solution(object):
    def climbStairs(self, n):
        """
        :type n: int
        :rtype: int
        """
        if n == 1:
            return 1
        a, b = 1, 2
        for i in xrange(2, n):
            tmp = b
            b = a+b
            a = tmp
        return b
